Large Diameter Flange

Large diameter flange refers to oversized pipe connection flanges generally above DN600, widely applied in heavy-duty industrial piping, municipal infrastructure and large-scale equipment supporting systems. Covering multiple types including large diameter weld neck flange, slip-on flange, plate flange, blind flange and lap joint flange, these components undertake connection, sealing and isolation tasks for large-caliber pipelines. Restricted by raw material size, forging capacity and machining difficulty, large diameter flanges adopt diversified forming processes different from conventional small-size flanges, and they occupy an essential position in long-distance transmission pipelines and large facility projects.

Large diameter flanges are manufactured in accordance with international standards such as ASME B16.47 Series A & B, GB/T 9113 and GB/T 9119. Abundant material options can be customized for various operating environments. Carbon steel large diameter flanges using A105, Q235B or 16Mn are widely adopted for water delivery, natural gas transmission, heating pipelines and wind power supporting equipment with remarkable cost advantages. Stainless steel large diameter flanges of F304 and F316L grades possess superior corrosion resistance, suitable for seawater transportation, sewage treatment and chemical industry large-caliber pipelines. Alloy steel large diameter flanges can be produced as customized products for high-temperature and high-pressure process pipelines in power plants and refineries. Conventional pressure classes range from Class 150 to Class 900. Raised face (RF) is the mainstream sealing form, and special RTJ sealing surfaces can be processed for high-pressure working conditions.

Three mainstream forming technologies are adopted for large diameter flanges: integral hot forging, steel plate cutting and rolling & welding forming. Integral forged large diameter flanges are used for high-pressure critical pipelines with high safety requirements. Plate cutting flanges are processed directly from extra-wide steel plates, mostly applied to low-pressure plate flanges. Roll-welded flanges are fabricated by rolling steel plates into circular rings followed by circumferential welding. Post-processing includes turning sealing surfaces, machining inner holes and drilling dense bolt holes. Stress relief heat treatment is necessary for roll-welded and thick-plate flanges to eliminate processing and welding residual stress. Every finished large diameter flange undergoes strict quality control, including flatness detection, dimensional tolerance inspection, ultrasonic non-destructive testing and welding seam inspection for spliced products to avoid deformation, cracks and incomplete fusion defects.

Large diameter flanges face unique technical challenges and possess distinct characteristics. The oversized structure brings higher requirements on flatness and rigidity. Uneven stress distribution easily causes sealing surface deformation under bolt preload and pipeline load, further triggering medium leakage. Therefore, higher precision machining standards and reasonable bolt arrangement design are required. Compared with small-size flanges, transportation and on-site installation are more complicated; hoisting tools and accurate alignment are essential during construction.

The outstanding value of qualified large diameter flanges lies in realizing reliable sealed connection for large-scale fluid conveying systems. They support the integration of long-distance trunk pipelines, reduce the layout limitation of large equipment interfaces and facilitate pipeline sectional installation, inspection and maintenance. Roll-welded large diameter flanges effectively break the size limitation of integral forging equipment and greatly shorten production cycles for extra-large specifications.

Large diameter flanges serve extensive engineering fields. They are core components for municipal water supply and drainage trunk lines, urban central heating networks, offshore seawater intake pipelines, natural gas transmission pipelines, power plant circulating water systems, desulfurization and denitrification environmental protection pipelines, and large storage tank piping. Carbon steel rolled large flanges dominate municipal and environmental protection projects, while stainless steel large diameter flanges are preferred for corrosive medium treatment systems.

During engineering selection, designers should comprehensively balance working pressure, medium characteristics, diameter size and project budget to choose forged, plate-cut or roll-welded structures reasonably. Low-pressure general pipelines can adopt economical rolled flanges, while high-pressure hazardous medium pipelines must select integral forged large diameter flanges to ensure long-term sealing stability.

With continuously mature rolling welding and heavy-duty machining technology, high-quality large diameter flanges provide stable connection solutions for oversized piping networks. As vital supporting fittings for large infrastructure and heavy industry projects, large diameter flanges guarantee safe and uninterrupted operation of large-caliber fluid transportation systems worldwide.